It is known to cool a piston of a heavy duty engine by directing a spray or stream of oil at its underside. For this purpose, a nozzle is secured to the engine block by means of a capscrew and communicates through the capscrew with an oil gallery in the engine block. Conventionally, the capscrew passing through a hole in the base or mounting collar of the nozzle serves as the means for correctly positioning and aligning the nozzle in the block but very accurate machining is required both in the drilling and in the tapping of the bore in the engine block on account of the precision with which it is essential to locate the oil nozzle. In this context, it should be noted that the clearance between the crankshaft, the connecting rod and the piston is typically 5 mm, but it can be as little as 3 mm.